Yuppies, the jig's up. As a voting bloc, you were a fiction of the politicians and the press; as trend-setters, you had everything except the only thing in politics -- sheer numbers.

You don't hold the key to the future alignment of power between the two parties -- but your downscale cousins, the "new-collar" voters, just might.

The new Democratic Policy Commission held its opening session yesterday and got a demographics lecture from a university professor who profiled this unheralded, in-between political class, enshrined them as the "swing voters of the 1980s," and faulted the Democrats for not even having them "on your political screens."

The commission, a 100-member body composed mainly of state and local elected officials, was created by Democratic National Chairman Paul G. Kirk Jr. to search for themes that will make the party "modern, moderate and mainstream."

The opening session didn't get too deep into new policy ideas, but it was presented with a road map for a new way of going after the electorate from Ralph Whitehead Jr., a University of Massachusetts professor and Democratic political consultant.

Whitehead's "new-collar" voters are baby boomers, age 21 to 45, who have family incomes between $20,000 and $40,000. They are clerks, shopkeepers, insurance agents, keypunchers -- the workhorses of the service economy.

They are the sons and daughters of blue-collar Americans; they inherited many of their parents' traditional values but, true to their generation, they are more comfortable with change than with the status quo. They make up 15 percent of the electorate, and they outnumber their more famous cogenerationists, the Yuppies (young urban professionals), by at least 6 to 1.

"You tell a new-collar voter about $600 toilet seats at the Defense Department and he'll want to fire the people involved," Whitehead joked. "You tell a Yuppie about one and he'll want to know what colors they come in."

What distinguishes these downscale Yuppies as political creatures, Whitehead said, is that they are up for grabs. Neither Democrat nor Republican, liberal nor conservative, they cannot be thought of as occupying the political center because there is no center with this "post-ideological" generation. "You make the middle and bring them to it," Whitehead advised. "You do it issue by issue."

Whitehead's list included 7 percent home mortgages, day care for the children of two-income families, clean air and water, and more college loans.

Other speakers had other lists, and if there was any theme to the session's rather amorphous rhetoric, it was that the global economy is changing, the voters know it, and the Democrats must identify themselves as the party that can best get out in front of that change.

"At least in the last campaign, the Republicans were able to tag us as the party of the status quo," said Kirk.

The session opened yesterday with each member present being called on to give a one-minute summary of the biggest challenge facing the country. The responses were revealing for what they left out. Of 55 speakers, only three mentioned arms control, one mentioned tax reform, and no one touched such social issues as abortion or crime. Economic development and education were the big winners.

Rep. Les Aspin (D-Wis.), chairman of the House Armed Services Committee, got as close as anyone to advancing a specific policy agenda when he told his fellow Democrats that "we ought to actually be for something in the defense area . . . instead of always appearing to be nibbling away at some major defense system."